Wyniki wyszukiwania - BazTech

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Numerical study of the ejection cooling mechanism of ventilation for a marine gas turbine enclosure

Shi Hong, Zhang Qianwei, Liu Meinan, Yang Kaijie, Yuan Jie

Polish Maritime Research

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2022

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nr 3

119--127

EN

A marine gas turbine enclosure must be designed to prevent overheating of the electrical and engine control components as well as diluting potential fuel leaks. In order to achieve an optimal enclosure design, a numerical study of the ventilation-ejection cooling mechanism of a gas turbine enclosure is carried out in this paper. The evaluation index of the ejection cooling performance is first proposed and the algorithm of numerical simulation is verified. On this basis, orthogonal combinations of structural parameters are carried out for the expansion angle α of the lobed nozzle and the spacing S between the outlet plane of the lobed nozzle and the inlet plane of the mixing tube. The flow and the temperature distribution inside the enclosure are analysed under different operating conditions. The results show that the influence of the lobed nozzle expansion angle α and the spacing S on the performance is not a single-valued function but the two influencing factors are mutually constrained and influenced by each other. For any spacing, the combined coefficient is optimal for the expansion angle α = 30°. When the expansion angle α = 45° and the spacing S = 100 mm, the combined coefficient and the temperature distribution inside the enclosure are optimal at the same time.

2

Thermal performance analysis of manned airships in a thermally variable environment

Shi Hong, Liu Meinan, Chen Jiamin, Zou Yitao

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2022

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Vol. 70, nr 5

art. no. e143105

EN

The safety and reliability of the manned airship depend to a considerable extent on its thermal performance. In this paper, heat balance equations are developed and solved in the C++ programming language. The temperature variation of the enclosure, gasbag, and nacelles of the manned airship is investigated. In addition, the effects of season, latitude, and orientation on the thermal performance of the manned airship and the airship nacelle are investigated. The results show that: (1) The average temperature difference of the nacelle surface at the same time is 25 K, while the maximum temperature difference in the nacelle is 29 K during the day, (2) the temperature distribution in the nacelle is similar in spring and autumn, with maximum temperature between 306 K and 309 K. The maximum temperature in the nacelle is between 300 K and 303 K in winter while the maximum temperature in the nacelles is between 309 K and 315 K in summer, (3) as the flight position of the manned airship changes from 20°N to 60°N, the average nacelle temperature varies slightly by about 1 K. However, as the latitude increases, the high- temperature region shifts from the bottom of the nacelle to the side of the nacelle, and (4) the temperature distribution of the upper envelope of the airship varies considerably with orientation. However, the average temperature of the nacelle is less impacted by orientation. These results are useful for understanding the thermal performance of manned airships.

3

Flow and heat transfer characteristics of a novel airfoil-based tube with dimples

Pei Houju, Liu Meinan, Yang Kaijie, Zhimao Li, Liu Chao

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2022

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Vol. 70, nr 4

art. no. e141984

EN

The performance of a novel airfoil-based tube with dimples is numerically studied in the present work. The effect of Reynolds number Re, dimples number N, relative depth H/D, and cross-distribution angle α on flow and heat transfer characteristics are discussed for Re in the range between 7,753 and 21,736. The velocity contour, temperature contour, and local streamlines are also presented to get an insight into the heat transfer enhancement mechanisms. The results show that both the velocity magnitude and flow direction change, and fluid dynamic vortexes are generated around the dimples, which intensify the flow mixing and interrupt the boundary layer, resulting in a better heat transfer performance accompanied by a certain pressure loss compared with the plain tube. The Nusselt number Nu of the airfoil-based tube increases with the increase of dimples number, relative depth, and Reynolds numbers, but the effect of cross-distribution angle can be ignored. Under geometric parameters considered, the airfoil-based tube with N = 6, H/D = 0.1, α = 0° and Re = 7,753 can obtain the largest average PEC value 1.23. Further, the empirical formulas for Nusselt number Nu and friction factor f are fitted in terms of dimple number N, relative depth H/D, and Reynolds number Re, respectively, with the errors within ± 5%. It is found that the airfoil-based tube with dimples has a good comprehensive performance.